linux-kernel - Re: [PATCH v3] virtio: Add platform bus driver for memory mapped virtio device

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Date:	Wed, 19 Oct 2011 13:27:20 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Pawel Moll <pawel.moll@....com>
Cc:	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"virtualization\@lists.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	Anthony Liguori <aliguori@...ibm.com>,
	"Michael S.Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3] virtio: Add platform bus driver for memory mapped virtio device

On Tue, 18 Oct 2011 10:44:35 +0100, Pawel Moll <pawel.moll@....com> wrote:
> > or actually specify it as
> > the power of 2 to use, (ie. valid values are 1 through 16, with 12 being
> > the value that virtio PCI would use).
> > 
> > Otherwise you have to do a divide on the qemu side.
> 
> Oh, really? My host-side implementation is just doing that:
> 
>         addr += align - 1;
>         addr &= ~(align - 1);

OK, so you're assuming power of 2.  Make sure you kill the guest or at
least the device if it's not though.

> \item The dynamic configuration changes, as described in p. 2.4.3
> ``Dealing With Configuration Changes'' are not permitted.

This means some devices simply won't work, at least in theory.  Why
don't you support this?

Thanks!
Rusty.
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